Anodic Gases Generated on a Carbon Electrode in Oxide-Ion Containing Molten CaCl2 for the Electro-Deoxidation Process

The gas generated on a commonly used carbon anode is highly related to the efficiency of electrolysis and the purity of cathodic products in molten CaCl2. Herein, the anodic gas generated on a carbon working electrode in a three-electrode setup was systematically analyzed using a gas chromatograph under controlled potentials in both molten CaCl2 and CaCl2-1 wt%CaO. Two successive oxidation steps of the graphite electrode were observed. The anodic gas contains both CO and CO2 with an atomic ratio (CO/CO2) of 0.076, 0.072, 0.073, and 0.144 under anodic potentials of 0V, 0.2V, 0.4V, and 0.6V (vs. Ag/AgCl) in molten CaCl2, respectively, while the atomic ratios of CO/CO2 are 3.639, 2.008, 1.666, 0.720 in molten CaCl2-1 wt%CaO. Therefore, CaO remarkably enhances the kinetics of the formation of CO and absorption of the generated CO2 forming CO32− that could decrease the efficiency of the electrolysis and purity of cathodic products.